Biscitraconimide copolymers with olefinically unsaturated materials

ABSTRACT

Curable bisimide compositions containing at least one biscitraconimide having general formula (I), wherein D is a divalent group, R is CH 2  --R 1 , and R 1  is independently selected from hydrogen and alkyl groups having 1-18 carbon atoms; at least one olefinically unsaturated material, and 0-15 mole percent, based on biscitraconimide of formula (I), of a cocurable material selected from the group consisting of bismaleimides, citraconic maleimides and itaconic maleimides, wherein the mole ratio of biscitraconimide of formula (I), to olefinically unsaturated materials is from 0.12 to 4.0; are disclosed. Also disclosed are copolymeric compositions of biscitraconimides and olefinically unsaturated materials, processes for making these copolymers and articles of manufacture embodying these copolymers. These copolymers exhibit improved thermostability, high glass transition temperature, are solvent resistant and are void-free. In addition, these curable materials are easily processed due to the large melt-cure window, low viscosity of the melt, low melting points of the biscitraconimides and the fact that curing can often be accomplished without additional solvents.

BACKGROUND OF THE INVENTION

The invention relates to curable biscitraconimide containingcompositions, copolymers of biscitraconimides with olefinicallyunsaturated materials, a process for curing these copolymers, and toarticles of manufacture comprising the biscitraconimide(co)polymers.

Biscitraconimides are known compounds and can be prepared by the methodsdisclosed in, "The Synthesis of Biscitraconimides andPolybiscitraconimides," Galanti, A. V. and Scola, D. A., Journ. of Poly.Sci.: Polymer Chemistry Edition, Vol. 19, pp. 451-475, (1981), thedisclosure of which is hereby incorporated by reference. Thesebiscitraconimides are polymerized to tough amber-colored films thatexhibit good thermal stability. In addition, the article points out thatNMR analysis shows that the observed ratio of methyl protons at 2.1 ppm.to the methylene protons at 1.6 ppm. in the biscitraconimides is lowerthan the theoretical ratios for the imide monomers. The difference isexplained as being due to a small degree of polymerization that couldoccur when the acid is dehydrated thermally.

"The Synthesis of Bisitaconamic Acids and Isomeric Bisimide Monomers,"Galanti, A. V. et al., Journ. Poly. Sci.: Polymer Chemistry Edition,Vol. 20, pp. 233-239 (1982) also discloses a method for the preparationof biscitraconimides in the form of an isomeric mixture of thecitraconic and itaconic imides.

In "The Development of Tough Bismaleimide Resins," Stenzenberger, H. D.,et al., 31st International SAMPE Symposium, Vol. 31, pp.920-932 (1986)it is disclosed that bismaleimides are prime candidates for carbon fiberreinforced composites because of their properties. However, the articlealso points out that these materials tend to be brittle. Thus, severalattempts have been made to improve the fracture toughness of thebismaleimides. First, the bismaleimides have been cocured with reactiveelastomers such as carboxy terminated acrylonitrile-butadiene rubbers.Also, the bismaleimide polymers have been modified with comonomers whichcopolymerize via a linear chain extension reaction and include bothdiene type copolymerization reactions and "ene"-type copolymerizationreaction. Thirdly, the bismaleimides have been modified withthermoplastic materials. Finally, the bismaleimides have been cured inthe presence of ionic curing catalysts such as imidazoles and tertiaryamines including diazobicyclo-octane (DABCO). Among the alternatives forimproving the fracture toughness of the bismaleimides was theincorporation of diallyl benzenes. As shown in table 3 it was found thatthese materials provided acceptable properties only up to 40 weightpercent of the maleimide. Once more than 40 weight percent of themaleimide was employed, a significant decrease in the flexural strengthand flexural modulus was observed.

In "Bismaleimide Resins the Properties and Processing of `Compimide` BMIResins," Segal, C. L., et al., 17th Nat. SAMPE Conference 17pp. 147-160(1985) formulated bismaleimides are modified withacrylonitrile-butadiene rubbers to produce an increased fracturetoughness. However, it was concluded that the rubber is not compatiblewith the base resin and an additional, pre-reaction step was necessaryto accomplish the modification.

Bismaleimide-styrene compositions are known from European PatentApplication 0 108,461 published on May 16, 1984, and, "MolecularStructure and Properties of Bismaleimide Styrene Cross-linkedCopolymers," Winter, et al., Proceedings of the 3rd Annual Int. Conf. onCrosslinked Polymers, Lucerne, Switzerland, pp, 291-303, (1989). ExampleII of the European Patent application also discloses a copolymer ofstyrene, acrylic acid, bismaleimide and biscitraconimide. However, thismaterial contains a relatively large amount of the bismaleimide andacrylic acid and thus is quite different from the material in accordancewith the present invention. Most importantly, the copolymer including abiscitraconimide disclosed in this patent application has a strain % of0.9, which is significantly lower than compositions of the presentinvention.

Finally, UK patent application GB 2,010,866 discloses copolymers ofstyrene with compounds having an N-substituted imide group includingbismaleimides and monomaleimides. In this patent it is briefly mentionedthat one of the possible imides that can be employed isN,N'-4,4'-diphenylmethane biscitraconimide. However, no examples usingthis compound are included, and this compound is an alkylated arylenebiscitraconimide.

Generally, the bismaleimide resins require difficult processingconditions, exhibit solvent retention in prepregs, have a high meltingpoint and high curing temperatures are required for the monomer. Inaddition, the maleimide polymers are often brittle due to the highcross-link density obtained in the network polymers. The foregoing bodyof prior art reflects the need for bisimide resin systems which areeasily processable and exhibit improved mechanical and physicalproperties.

SUMMARY OF THE INVENTION

The present invention has for its object to eliminate the foregoingdrawbacks of the prior art bisimide resins and to substantially improvethe thermal properties of molded compositions made from bisimide resins.In addition, it is an object of the present invention to providebisimide copolymers having low curing temperatures which are easilyprocessible, often without an additional solvent. For this purpose thepresent invention provides curable bisimide compositions containing atleast one biscitraconimide having the general formula ##STR1## wherein Dis a divalent group, R is CH₂ --R₁, and R₁ is independently selectedfrom hydrogen and alkyl groups having 1-18 carbon atoms; at least oneolefinically unsaturated material selected from the group consisting ofstyrene, α-methyl styrene, β-pinene, indene, divinyl benzene, propenylbenzene, isopropenyl benzene, substituted styrenes, triallyl cyanurate,triallyl isocyanurate,stilbene, dibenzalacetone and mixtures thereof;and 0-15 mole percent, based on biscitraconimide units of the formula I,of a cocurable material selected from the group consisting ofbismaleimides, citraconic maleimides and itaconic maleimides, whereinthe mole ratio of biscitraconimide units to olefinically unsaturatedmaterial is from 0.12 to 4.0. The present invention also relates tocopolymeric compositions of biscitraconimides and olefinicallyunsaturated materials, processes for making these copolymers andarticles of manufacture embodying these copolymers including articlescomprising fibrous reinforcement and prepregs.

These polymeric compositions and the articles of manufacture producedtherefrom offer several advantages over prior art bisimide formulations.For example, these biscitraconimide-containing materials can beprocessed at lower temperatures than bismaleimides and the resultantpolymers show improved properties, including a high T_(g) and goodthermostability. Further, the mechanical properties of these materialsare significantly better than expected from similar, commerciallyavailable materials.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Biscitraconimides are known compounds and can be prepared by any of themethods disclosed in Dutch Patent Application No. 6,514,767; "TheSynthesis of Biscitraconimides and Polybiscitraconimides", Galanti, A.V., and Scola, D. A., Journ, of Polym. Sci.: Polymer Chemistry Edition,Vol. 19, pp. 451-475 (1981); and "The Synthesis of Bisitaconamic Acidsand Isomeric Bisimide Monomers", Galanti, A. V., et al., Journ. ofPolym. Sci.: Polymer Chemistry Edition, Vol. 20, pp. 233-239 (1982), thedisclosures of which are hereby incorporated by reference.

The aliphatic biscitraconimides employed in the present inventioncomprise biscitraconimide compounds having the formula I: ##STR2##wherein D is a divalent group, R is CH₂ --R₁, and R₁ is independentlyselected from hydrogen and alkyl groups having 1-18 carbon atoms.

D may be selected from divalent groups including alkylene,cyclicalkylene, arylated alkylene groups, oligomers ofbiscitraconimides, and residues of one or more cocurable materials andbiscitraconimide oligomers. D is preferably selected from a substitutedor unsubstituted aliphatic divalent group. Most preferably D is adivalent group selected from ethylene, propylene, methylene, butylene,2-methylpentylene, hexylene, dimethylene cyclohexane, m-xylylene; andtricyclodocecylene.

Arylated alkylene groups are groups wherein the two radicals forming thedivalent radical D are obtained by extracting hydrogens from alkylcarbon atoms and at least one of the alkyl carbon atoms have one or moreof their remaining hydrogen atoms substituted by an aryl group.

Suitable aliphatic biscitraconimides are in particular

N,N'-ethylene-biscitraconic imide;

N,N'-hexamethylene-biscitraconic imide;

N,N'-tetramethylene-biscitraconic imide;

N,N'2-methyl-pentamethylene-biscitraconic imide;

N,N'-propylene-biscitraconic imide;

N,N'-4,4'-dicyclohexylmethane-biscitraconic imide;

N,N'-meta-xylylene biscitraconimide;

N,N'-dicyclohexyl-biscitraconic imide; and

N,N'-α,α'-4,4'-dimethylene cyclohexane-biscitraconic imide.

The olefinically unsaturated materials useful in the present inventioninclude styrene, substituted styrenes, styrene derivatives, triallylcyanurate, triallyl isocyanurate, and mixtures thereof. Particularlyuseful styrene derivatives include α-methyl styrene, β-pinene, indene,divinyl benzene, stibene, dibenzalacetone, propenyl benzene andisopropenyl benzene. The most preferred olefinically unsaturatedmaterials for use in the present invention are styrene, styrenederivatives, substituted styrenes and mixtures thereof.

The curable composition may also comprise one or more cocurablematerials. Suitable cocurable materials include bismaleimides,citraconic maleimides, itaconic maleimides, citraconic/itaconicmaleimides, citraconimides, itaconimides, tris-citraconimides,tris-itaconimides, bisitaconimides, aryl biscitraconimides and alkylatedarylene biscitraconimides. Alkylated arylene biscitraconimides arebiscitraconimides wherein the citraconimide units are joined by arylradicals having one or more of the aromatic hydrogen atoms replaced byalkyl groups. For example, N,N'-4,4'-diphenylmethane biscitraconimide isan alkylated arylene biscitraconimide.

When the cocurable material is a maleimide-containing cocurablematerial, it preferably comprises from 0 to 15 mole percent based on thebiscitraconimide of the formula I, of the composition, and morepreferably is not present in the composition of the present invention.The remaining listed cocurable materials are often present as impuritiesin biscitraconimide compositions. They may be present in amounts of from0-50 mole percent based on the biscitraconimide of the formula I, andmore preferably comprise 1-30 mole percent based on the biscitraconimideof the formula I.

The present invention also embodies cured polymeric materials comprisingunits derived from at least one biscitraconimide of the formula (I);units derived from at least one olefinically unsaturated material; andfrom 0-15 molar percent, based on the biscitraconimide of the formula I,of units derived from one or more cocurable materials selected frombismaleimides, citraconic maleimides, and itaconic maleimides, whereinthe mole ratio of units derived from the biscitraconimide of the formulaI to units derived from olefinically unsaturated material is from 0.12to 4.0. More preferably, the maleimide-containing cocurable materialsare not present in the composition and the mole ratio of units derivedfrom the biscitraconimide(s) of the formula I to units derived fromolefinically unsaturated material(s) is from 0.25 to 1.35.

These cured polymeric materials may optionally include 0-50 molarpercent, based on the biscitraconimide of the formula I, of unitsderived from at least one cocurable material selected from the groupconsisting of citraconic/itaconic imides, bisitaconimides,citraconimides, itaconimides, tris-citraconimides, tris-itaconimides,aryl biscitraconimides, and alkylated arylene biscitraconimides. Morepreferably, these cocurable materials make up 1-30 molar percent of thecomposition based on the biscitraconimide of the formula I.

Curing may be accomplished thermally or radically, and results in acopolymer of biscitraconimide and the olefinically unsaturated material.At a molar ratio of biscitraconimide to olefinically unsaturatedmaterial of 0.5, an alternating copolymer is obtained. All other ratiosgive some homopolymerization of one of the units.

The curable aliphatic biscitraconimide mixtures with olefinicallyunsaturated materials, and particularly those with styrene, substitutedstyrenes and styrene derivatives, have fairly low clear points due tothe excellent solubility of the aliphatic biscitraconimides in thesematerials, as well as the low melting points of the biscitraconimides.

The curable composition of the present invention may be cured in thepresence of a curing catalyst. The curing is carried out by simplyheating a composition containing at least one aliphatic biscitraconimideof the formula (I), an olefinically unsaturated material, a curingcatalyst and, optionally, a cocurable material, to a temperaturesufficient to cocure the biscitraconimide and the olefinicallyunsaturated material, and maintaining the temperature at that level fora sufficient time to cure the material into a cured polymeric product.Curing can be accomplished at 20° C. to 250° C. Generally, the curingwill be accomplished at a temperature in excess of 130° C. The curingtime will vary depending upon the presence or absence of curing catalystand type of material present. Conventional curing catalysts formaleimide, itaconimide and citraconimide compositions may be employed.For example, peroxides may be used to catalyse curing at lowertemperatures of 20°-120° C., depending on the particular peroxideselected.

The copolymers can be formed without the use of solvents, and novolatiles are formed during the curing reaction, which results invoid-free copolymers. The copolymers show improved properties. Forexample, the thermostability is higher than that expected fromstyrene-containing commerially available systems. In addition, the T_(g)values are somewhat higher than for commercially available systems.Further, the copolymers of the present invention are solvent resistant,and simple, monounsaturated materials such as styrene may be usedwhereas in other systems complex bis-styrenes are required.

The cured polymeric product of the present invention is particularlyuseful in resin transfer molding and fiber-reinforced composites becauseof its excellent properties. As a result, a novel composition isobtained which is easily processable due to the low melting points ofthe biscitraconimides of the formula I. In addition, thebiscitraconimides of the formula I have a large melt cure window whichallows them to be more readily cocured with a large group of materialswhich would not be cocurable with bismaleimides because a curingtemperature suitable for both the bismaleimide and the cocurablematerial could not be found. Finally, the biscitraconimide melt itselfhas a low viscosity which renders it easier to handle thanbismaleimide-based melts.

For applications in the laminate field, it is necessary to make prepregsfrom the biscitraconimides in order to obtain the desired properties forthe laminate. The impregnated fibre cloth must be tack-free, flexibleand have the proper melt viscosity. The biscitraconimide monomersthemselves are not suitable for these applications since they are eitheroils or are too crystalline in nature.

It is possible to make prepolymers having the desired properties whichcan be employed to make prepregs with the distinct advantage that thesepolymers do not require a solvent in the prepreg manufacturing process.In the present commercial prepreg manufacturing methods, solvents mustbe employed which leads to costly solvent removal steps and some voidsin the final product.

The invention will be further described with reference to the followingexamples which are not to be construed as limiting the scope of theinvention.

EXAMPLE 1

30 grams of 1,6-N,N'-hexyl biscitraconimide and 20 grams of styrene aremixed at a temperature of 100° C. (molar ratio of biscitraconimide tostyrene of 0.5). The mixture is poured into a preheated mold at 120° C.to prepare an unreinforced sheet of 10×10×0.3 cm. The temperature isslowly increased up to 180° C. and held for three hours. The flexuralproperties, T_(g), and TGA values are given in table 1.

EXAMPLE 2

21 grams of 1,6-N,N'-hexyl biscitraconimide and 29 grams of styrene aremixed at a temperature of 100° C. (molar ratio of 0.25). The mixture ispoured into a preheated mold and cured as described in Example 1. Theproperties of the unreinforced sheet are also given in table 1.

EXAMPLE 3

43 grams of 1,6-N,N'-hexyl biscitraconimide and 7 grams of styrene aremixed at a temperature of 100° C. (molar ratio of of 2.0). The mixtureis poured into a preheated mold and cured as described in Example 1. Theproperties of the unreinforced sheet are also given in table 1.

EXAMPLE 4

37.5 grams of 1,5N,N'-2-methylpentyl biscitraconimide and 12.5 grams ofstyrene are mixed at 60° C. (molar ratio of 1.0). After cooling themixture to room temperature the mixture retains its low viscosity andcan be easily poured into a mold to prepare unreinforced sheets asdescribed in Example 1. The properties of this unreinforced sheet aregiven in table 1.

EXAMPLE 5

28.5 grams of N,N'-1,6-hexyl biscitraconimide, 16.5 grams ofα-methylstyrene and 5.0 grams of styrene are mixed at 100° C. Themixture is poured out in a preheated mold and cured as described inExample 1. The properties of the unreinforced sheet are given in table1.

EXAMPLE 6

30 grams of N,N'-1,6-hexyl biscitraconimide, 15.5 grams of styrene and4.5 grams of triallylcyanurate are mixed at 110° C. The mixture ispoured into a preheated mold and cured by the procedure described inExample 1. The properties of the unreinforced sheet material are givenin table 1.

EXAMPLE 7

29.5 grams of N,N'-meta xylylene biscitraconimide and 20.5 grams ofstyrene are mixed at 110° C. The mixture is poured into a preheated moldand cured as described in Example 1. The properties of the unreinforcedsheet are given in table 1.

                  TABLE 1                                                         ______________________________________                                        geltime      flexuraltest           TGA                                               (min) at Emod           Tg      at 400 C                              example 130° C.                                                                         GPA     strain %                                                                             (DMA)   (%)                                   ______________________________________                                        1       7        2.9     2.5    235     3.8                                   2       5        3.0     1.1    240     7.3                                   3       16       2.8     4.0    185     5.4                                   4       6        2.7     3.0    --      4.0                                   5       27       3.1     2.0    --      24.8                                  6       1.5      3.4     2.0    250     4.4                                   7       2.5      3.6     2.2    240     3.0                                   ______________________________________                                    

EXAMPLE 8 Preparation of Glass Reinforced Sheet Material by ResinTransfer Molding

In order to prepare a 1.6 mm thick glass-reinforced sheet, 10 plies ofglass fabric with a suitable sizing are placed in a plain mold. The moldis closed and heated up to 100° C. A mixture of 1,6-N,N'-hexamethylenebiscitraconimide and styrene in a molar ratio of 0.5 is injected at 100°C. with a pressure of 3 bar. The mold is filled within 3 minutes.

For curing, the temperature is raised to 130° C. and maintained for 1hour. Afterwards, the temperature is again increased to 180° C. andmaintained for 3 additional hours. The resultant composite materialcontains 43 vol % of glass. The material exhibited an E-modulus of 15.1GPa, a maximum strength of 327 MPa, and an elongation at break of 2.6 ina flexural test. The material also had a dielectric constant of 3.9.

EXAMPLE 9

30 grams of 1,5 N,N'-2-methylpentamethylene biscitraconimide and 20grams of styrene containing 0.05 grams of a peroxide initiator, Perkadox16 (Bis(4-tert-butyl cyclohexyl) peroxydicarbonate ) are mixed at roomtemperature. The mixture showed, according to the SPI test (ISO R584),carried out at 50° C., an exotherm of about 172° C. after 23 minutes.The mixture is poured into a mould and cured at 50° C. for 2 hours. Theproperties have been messured after postcuring at 180° C. (3 hours) and230° C. (4 hours). The properties, HDT and flexural characteristics, aregiven in table 2.

                  TABLE 2                                                         ______________________________________                                                flexuraltest                                                          example   E mod   Bend str    strain                                                                              HDT                                       no.       N/mm.sup.2                                                                            N/mm.sup.2  %     C                                         ______________________________________                                         9        3300    100         3.6   >225                                      10        3100    108         4.3   >225                                      11        3500    100         3.3   >225                                      12        3400    111         6.5    180                                      ______________________________________                                         *Flexural properties have been measured according ISO 178.                    *Heat Distortion Temperature according ISO R 75, method A.               

EXAMPLE 10

35 grams of 1,5 N,N'-2-methylpentamethylene biscitraconimide and 15grams of beta-pinene containing 0.5 grams of Trigonox 145 are mixed atroom temperature; the molar ratio biscitraconimide to beta-pinene being1.2. The mixture is poured into a mould and cured at 140° C. to preparean unreinforced sheet 15×15×0.4 cm. after gelation the temperature isincreased up to 180° C. and held for 3 hours. After postcuring at 230°C. for 4 hours the properties have been determined (see table 2 ).

EXAMPLE 11

A mixture of 25.5 grams of 1,5-N,N'-2-methylpentamethylenebiscitraconimide and 4.5 grams of 4,4'-N,N'-methylenedianalinebismaleimide (MDA BMI) is made homogeneous at about 100° C. Aftercooling to room temperature, 20 grams of styrene containing 0.05 gramsof Perkadox 16 and 0.25 grams of Triganox 145 is added to the mixture ofbisimides. The molar ratio of bisimide to styrene being 0.5. Accordingto the SPI test, carried out at 50° C., the exotherm appeared after 14minutes and was at 156° C. The mixture is pured into the mould and curedat 50° C. (1 hour) and 140° C. (2 hours). The properties have beendetermined after a post curing of 4 hours at 230° C. (see table 2).

EXAMPLE 12

40 grams of 1,6 N,N'-2,2,4-trimethylhexamethylene biscitraconimide and10 grams of diisopropenyl benzene are mixed at a temperature of 40° C.To the mixture a peroxide, Trigonox 145 (1.5%) and 1,4 diazo-bicyclooctane (1.0%) have been added. The ratio of biscitraconimide to theolefinic unsaturated bonds is 0.9. The mixture is poured into a mouldand cured at 140° C. After gelation, the temperature is increased up to180° C. and held for 2 hours. The properties have been determined aftera postcuring at 230° C. for 3 hours. (see table 2).

The foregoing description and examples of the invention have beenpresented for the purpose of illustration and description only and arenot to be construed as limiting the invention to the precise formsdisclosed. The scope of the invention is to be determined by the claimsappended hereto.

What is claimed is:
 1. A composition comprising at least onebiscitraconimide having the formula ##STR3## wherein D is a divalentgroup, R is CH₂ --R₁, and R₁ is selected from the group consisting ofhydrogen and alkyl groups having 1 to 18 carbon atoms; at least oneolefinically unsaturated material; selected from the group consisting ofstyrene, α-methyl styrene, β-pinene, indene, divinyl benzene, propenylbenzene, isopropenyl benzene, substituted styrenes, triallyl cyanurate,triallyl isocyanurate, stilbene, dibenzalacetone and mixtures thereof;and from 0-15 mole percent based on the biscitraconimide of the formulaI of a cocurable material selected from the group consisting ofbismaleimides, citraconic maleimides, and itaconic maleimides; whereinthe mole ratio of said biscitraconimide of the formula I, to saidolefinically unsaturated material is from 0.12 to 4.0.
 2. A compositionaccording to claim 1 wherein said at least one biscitraconimide of theformula I is selected from the group consisting of alkylenebiscitraconimides, cyclicalkylene biscitraconimides, and arylatedalkylene biscitraconimides.
 3. A composition according to any one ofclaims 1 and 3 wherein D is selected from the group consisting ofmethylene, ethylene, propylene, butylene, 2-methylpentylene, hexylene,meta xylylene, tricyclododecylene, and dimethylene cyclohexane.
 4. Acomposition according to any one of claims 1 and 2-3 wherein saidolefinically unsaturated material is selected from the group consistingof styrene and mixtures of styrene with one or more of indene, α-methylstyrene, β-pinene, divinyl benzene, stilbene, dibenzalacetone,isopropenyl benzene and propenyl benzene.
 5. A composition according toany one of claims 1 and 2-4 wherein the mole ratio of saidbiscitraconimide of the formula I to said olefinically unsaturatedmaterial is from 0.25 to 1.35.
 6. A composition according to any one ofclaims 1 and 2-5 further comprising up to 50 mole percent, based on thebiscitraconimide of the formula I, of a material selected from the groupconsisting of citraconic/itaconic imides, bisitaconimides, itaconimides,citraconimides, tris-citraconimides, tris-itaconimides, aromaticbiscitraconimides, and alkylated arylene biscitraconimides.
 7. A processfor the preparation of a copolymer containing at least one unit derivedfrom a biscitraconimide and at least one unit derived from anolefinically unsaturated material, characterized in that a compositionaccording to one or more of claims 1 and 2-6 is cured at a temperatureabove the melting point of the biscitraconimide unit.
 8. An article ofmanufacture obtained by curing one or more of the compositions accordingto claims 1 and 2-6.
 9. An article of manufacture according to claim 8further comprising fibrous reinforcement.
 10. A prepreg obtained byimpregnating fibers with one or more of the compositions of claims 1 and2-6 and curing the impregnated material at an elevated temperature. 11.A copolymeric composition comprising at least one unit derived from abiscitraconimide having the formula: ##STR4## wherein D is a divalentgroup, R is CH₂ --R₁ and R₁ is independently selected from the groupconsisting of hydrogen and alkyl groups having 1-18 carbon atoms; atleast one unit derived from an olefinically unsaturated material fromthe group consisting of styrene, substituted styrene, α-methyl styrene,β-pinene, indene, divinyl benzene, stilbene, dibenzalacetone, propenylbenzene, triallyl cyanurate, triallyl isocyanurate, isopropenyl benzeneand mixtures thereof; and from 0 to 15 molar percent based on thebiscitraconimide units of the formula I, of a cocurable materialselected from the group consisting of bismaleimides, citraconicmaleimides and itaconic maleimides, wherein the molar ratio of unitsderived from biscitraconimide of the formula I to units derived fromolefinically unsaturated material is from 0.12 to 4.0.
 12. A polymericcomposition as claimed in claim 11 wherein said at least one unitderived from a biscitraconimide of the formula I is selected from thegroup consisting of alkylene biscitraconimides, cycloalkylenebiscitraconimides and arylated alkylene biscitraconimides.
 13. Apolymeric composition as claimed in any one of claims 11-12 wherein D isa divalent group selected from the group consisting of methylene,ethylene, propylene, butylene, 2-methylpentylene, hexylene, dimethylenecyclohexane, meta-xylylene and tricyclododecylene.
 14. A polymericcomposition as claimed in any one of claims 11-12 and 13 furthercomprising up to 50 molar percent, based on the biscitraconimide unitsof the formula I, of a cocurable material selected from the groupconsisting of citraconic/itaconic imides, bisitaconimides, itaconimides,citraconimides, tris-citraconimides, tris-itaconimides, aromaticbiscitraconimides, and alkylated arylene biscitraconimides.
 15. Apolymeric composition as claimed in any one of claims 11-12 and 13-14wherein the molar ratio of units derived from biscitraconimide of theformula I to units derived from olefinically unsaturated material isfrom 0.25 to 1.35.